The invention relates to a hydro-pneumatic spring, consisting of a cylinder, a plunger movable in it, a chamber connected with the cylinder, containing a gas cushion and for the rest filled with liquid and means for controlling the amount of liquid present in the chamber.
Such springs are applied in vehicles in particular, because at the slight stiffness desired they do not have the disadvantage that between the empty and fully loaded condition of the vehicle there is a great difference in compression of the springs, as this compression is compensated by the liquid control. Consequently the springs have a great stiffness in respect of the average static load and a small stiffness in respect of the fluctuating, dynamic loads.
With spring systems of this type known in the art the liquid control is effected by means of valves, slides and such control members that are mechanically coupled with the plunger and that, dependent upon the position of the plunger in respect of the cylinder, connect the cylinder or the chamber connected with it with a fluid supply or discharge. These spring systems known in the art are, however, rather complicated and expensive and require much attendance and maintenance.